In electrophotographic applications such as xerography, a charge retentive surface is electrostatically charged and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder imaging material referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to transfer, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known and useful for light lens copying from an original and printing applications from electronically generated or stored originals, where a charged surface may be imagewise discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a charge retentive substrate operate similarly.
Although a preponderance of the toner forming the image is transferred to the paper during the transfer step, some toner invariably remains on the charge retentive surface, it being held thereto by relatively high electrostatic and/or mechanical forces. Additionally, paper fibers, Kaolin and other debris have a tendency to be attracted to the charge retentive surface. It is essential for optimum operation that the toner remaining on the surface be cleaned thoroughly therefrom. Blade cleaning is a highly desirable method for removal of residual toner and debris (hereinafter, collectively referred to as "toner") from a charge retentive surface, because it provides a simple, inexpensive structure compared to the various fiber brush or magnetic brush cleaners that are well known for dry electrophotography. In a typical application, a relatively thin elastomeric blade member is provided and supported adjacent and transversely across a moving charge retentive surface with a blade edge chiseling or wiping toner from the surface. Subsequent to release of toner from the surface, the released toner accumulating adjacent to the blade is transported away from the blade area by a toner transport arrangement or by gravity. Unfortunately, blade cleaning suffers from certain deficiencies, primarily resulting from the frictional sealing contact which must be maintained between the blade and the charge retentive surface. Friction between the surfaces causes wearing away of the blade edge. Cleaning blades might also be used for the removal of toner from the surface of a detoning roll used to collect toner from the bristles of a brush cleaner, as shown for example in U.S. Pat. No. 4,819,026 to Lange et. al., and assigned to the same assignee as the present application.
In addition to the problem of wear, which is more or less predictable over time, blades are also subject to unpredictable failures. The impact from carrier beads remaining on the charge retentive surface subsequent to development may damage the blade, and sudden localized increases in friction between the blade and surface may cause the phenomenon of tucking, where the blade cleaning edge becomes tucked underneath the blade, losing the frictional sealing relationship required for blade cleaning. Additionally, slight damage to the contacting edge of the blade appears to eventually initiate tearing sites. These problems require removal and replacement of the blade.
Investigation into the characteristic of cleaning blade performance has shown that lateral conformance of the blade, i.e., conformance of the blade across the imaging surface, is generally given by EQU .epsilon..varies.1/E
where
.epsilon. is blade conformance in microns; PA1 E is the Young's modulus for a given elastomer. PA1 .omega..sub.0 is the resonant frequency of the blade.
A high value for lateral conformance is very desirable, and accordingly, for a given blade, Young's modulus should be small.
It has also been determined that for the blade to optimally respond to roughness in the imaging surface, particularly at high speeds, the resonant frequency of the blade must be as high as possible. Resonant frequency of a blade is given by EQU .omega..sub.0 .varies..sqroot.E
where
A high resonant frequency for optimal frequency response is very desirable, and accordingly, for a given blade, Young's modulus for the selected elastomer should be large.
It can be seen that the use of isotropic materials, such as the urethane cleaning blades currently used in electrophotographic cleaning processes, requires a trade off in the selection of materials having a Young's modulus that satisfactorily meets both the lateral conformability requirement, and the resonant frequency requirements.
"Impregnated Poromeric Material Cleaning Blade, " Xerox Disclosure Journal, Spencer et. al., Vol. 1, No. 4, Apr. 1976, p. 79, suggests a cleaning blade composition of non-woven polyester fibers bound together in polyurethane, for the improvement of abrasion resistance, hardness, resilience, and load bearing capacity. U.S. Pat. No. 2,767,529 to Scott suggests a doctor blade for paper making machines made of metal or layers of fabric bonded together by synthetic resin. U.S. Pat. No. 3,635,556 to Levy suggests a backing pad made of a carbon filled plastic foam material. "Nylon Fiber Reinforcement for Polyurethane Composites," Polymer Composites, Cordova et. al., Vol. 8, No. 4, Aug. 1987, pp. 253-255, suggests polyurethane thermoset material with a nylon fiber filler for improved impact strength, impact fatigue and decreased stress cracking.